mmacleod1983 Posted September 27, 2015 Report Share Posted September 27, 2015 First time posting to the forum but long time browser! Anyway. I have a 3 channel JBL amp rated at 75x2 and 500x1 rms at 2 ohms. No problems. I put a multi meter on my amp while it is off and I get a nominal reading of 2.4 ohms on the subwoofer side and roughly 2.1 on the stereo side. When I turn on the amp, but with the head unit off, I get negative resistance of -2.2 ohms and the same on the stereo side of roughly -2.3 ohms. If I touch the positive to positive lead and negative to negative. If I place the negative lead of my multimeter to the positive terminal of the amp I get positive resistance. Is this normal? Why would I have negative resistance if the amp is on, but positive resistance if off? Any why would touching the leads opposite change this back to positive resistance? Is this something to do with the circuitry of the amp? My subs are not moving or playing any signal through them. Is this normal to have negative resistance while the amp is turned on? Link to comment Share on other sites More sharing options...
SnowDrifter Posted September 27, 2015 Report Share Posted September 27, 2015 You can't measure resistance on an energized circuit. I'm surprised you didn't fry your multi meter to be honest You're getting a bogus reading as the meter isn't designed for this scenario ~~~~~~~~SAY NO TO PHOTOBUCKET~~~~~~~~ Snow's DD-1 tracks here: https://www.stevemeadedesigns.com/board/topic/167433-snows-dd-1-tracks/ My take on OFC vs CCA: https://www.stevemeadedesigns.com/board/topic/110381-things-that-piss-you-off-in-the-car-audio-world/?do=findComment&comment=2461444 Link to comment Share on other sites More sharing options...
mmacleod1983 Posted September 27, 2015 Author Report Share Posted September 27, 2015 thanks for the lesson learned Obviously I dont know how to use a multimeter haahaha Glad you told me becasue I thought I had fried my sub or amp circuitry Link to comment Share on other sites More sharing options...
mmacleod1983 Posted September 27, 2015 Author Report Share Posted September 27, 2015 thanks for the lesson learned Obviously I dont know how to use a multimeter haahaha Glad you told me becasue I thought I had fried my sub or amp circuitry Link to comment Share on other sites More sharing options...
audiofanaticz Posted September 27, 2015 Report Share Posted September 27, 2015 I'm surprised you didn't fry your multi meter to be honest If that happens you have more serious problems with your multimeters, since they can handle being plugged into 110v, 220v, and 480+ volt electrical outlets. Link to comment Share on other sites More sharing options...
SnowDrifter Posted September 27, 2015 Report Share Posted September 27, 2015 I'm surprised you didn't fry your multi meter to be honest If that happens you have more serious problems with your multimeters, since they can handle being plugged into 110v, 220v, and 480+ volt electrical outlets. Last time I measured resistance on a live circuit that function didn't work any more. And that was with my Klein meter ~~~~~~~~SAY NO TO PHOTOBUCKET~~~~~~~~ Snow's DD-1 tracks here: https://www.stevemeadedesigns.com/board/topic/167433-snows-dd-1-tracks/ My take on OFC vs CCA: https://www.stevemeadedesigns.com/board/topic/110381-things-that-piss-you-off-in-the-car-audio-world/?do=findComment&comment=2461444 Link to comment Share on other sites More sharing options...
reedal Posted September 27, 2015 Report Share Posted September 27, 2015 Yeah, you're not supposed to measure resistance on a live circuit. Don't know why, just what I was always taught. Just like you don't read current parallel, only in series. Don't know why, but someone working with electricity and electronics much longer than me said no so I listened SMD Tool Map https://www.stevemeadedesigns.com/board/topic/193176-smd-tool-map-new-november-2014/ Build log https://www.stevemeadedesigns.com/board/topic/197217-reeds-03-tahoe-hat-sqaq-singer-xs-shca-cockbox-80prs/?page=32 Link to comment Share on other sites More sharing options...
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